Editorial

To date, there are still many open questions regarding feasible conservation treatments counteracting paper degradation caused by copper-containing pigments, most notably, verdigris. We are therefore delighted to present this issue of Restaurator dedicated to research related to verdigris. To advance our understanding of the processes taking place during ageing of verdigris, we will first present a paper by Lynn Brostoff and Cynthia Connelly Ryan who explored the natural alteration of both neutral and basic forms of the pigment. We will then progress and introduce two approaches to treating verdigris-damaged paper. Leah Humenuck tested a rigid gel application of benzotriazole (BTA), a complexing agent, on historical samples, while Jasna Malešič et al. studied the efficacy of several commercially available deacidification agents as well as the antioxidant tetrabutylammoniumbromide (TBAB). Finally,we conclude this volume with amore art technologically focussed contribution. Maria Plate et al. investigated the green paint layer of a Japanese folding screen from the Edoperiod and discuss on this basis the production, use and designation of historic Japanese green pigments. Within the last 10 years, much effort was dedicated to further research verdigris, and one might think that the time has come to compile findings and move forward to recommendations for specific treatments and conservation methodology in general. Recent studies in art technology allow the conclusion that oftentimes, historic recipes and current sample design might not always match. In her study of the alterations of verdigris published in the first volume of Restaurator 2020, Brostoff and Connelly Ryan give an overview of historical recipes for verdigris and the resulting compounds. The manufacture of verdigris typically involved the corrosion of copper sheets with acetic acid. Additives and different production methods not only produce a variety of blue to green copper compounds, but also two structurally distinct types of verdigris: the neutral copper acetate monohydrate and a series of basic copper acetate hydroxide salts.